Cathode for electrical discharge tubes



1957 H. KATZ ETAL CATHODE FOR ELECTRICAL DISCHARGE TUBES Filed March 10, 1955 flye fors.

Jaw gm 1 a United States Patent CATHODE FOR ELECTRICAL DISCHARGE TUBES Helmut Katz and Siegfried Costa, Munich, Germany, assignors to Siemens & Halske Aktiengesellschaft, Munich and Berlin, Germany, a German corporation Application March 10, 1953, Serial No. 341,514

Claims priority, application Germany March 24, 1952 4 Claims. (Cl. 313-346) This invention is concerned with a dispenser type cathode for electrical discharge tubes.

In known cathodes of this type, the emissive material migrates in operation through a retaining wall forming the emitting surface. Such wall has in known cathodes of this kind a porous structure or is otherwise provided with fine passages. Sintered tungsten or molybdenum bodies are oftentimes used. Barium or thorium compositions or alloys made of such substances dilfuse through the pores or fine passages of the corresponding wall and migrate thus to the emitting surface formed thereby for distribution thereon.

It has now been discovered that metallic thorium can diffuse through a dense metallic sheet, the term dense being used in the customary sense, meaning a sheet having a dense or compact structure substantially free of pores or fissures. The invention recognizes this discovery and proposes to provide a cathode of the dispenser type comprising a receptacle containing thorium as an emissive material, and having a retaining wall made of a relatively dense sheet of molybdenum or similar high melting metal. The emissive thorium material diffuses through the dense sheet of the retaining wall to the emitting surface formed thereby. The sheet may be up to several tenths of a millimeter thick, even more, if correspondingly long times for forming and high forming temperatures can be provided for or tolerated.

An example of the invention is illustrated in the accompanying drawing.

Referring now to the drawing, the cathode diagrammatically shown therein is a flat indirectly heated cathode. The emissive material 1, which may be thorium or a known thorium" composition or alloy, is disposed inside of a pot-shaped receptacle having a retaining wall 2 and closed on top by a thin metallic sheet 3 of dense structure, such sheet forming the emitting surface. The thickness of the sheet will depend on the size and geometric form thereof, which may of course vary, and amounts at the most to several tenths of a millimeter, that is, in any case less than one millimeter. The sheet 3 may be made of molybdenum or a similar metal of high ice melting point. The emissive thorium-containing substance 1 difluses in the operation of the cathode through the dense sheet 3, thus migrating to the emitting surface formed thereby. The retaining wall 2 of the pot-shaped receptacle is thicker than the sheet 3 so as to inhibit as much as possible diffusion of the emissive substance therethrough.

The cathode is mounted on a tubular member 4 which also serves as a heat radiation shield.

The cathode is heated by a heater coil 5 which is in usual manner provided with an insulating layer 6.

Changes may be made within thc scope and spirit of the appended claims.

We claim:

1. An indirectly heated dispenser type cathode for electrical discharge tubes having a receptacle for holding a normally migratory emissive material of the class of thorium, said receptacle comprising a metallic retaining wall and a cover sheet made of high melting metallic material of relatively dense structure substantially free of pores and fissures, said cover sheet being less than one millimeter thick and forming with said retaining wall which is thicker than said sheet an interiorly unobstructed cavity containing said emissive material, the outside of said cover sheet forming the emitting surface of said cathode, diffusion of said emissive material through said retaining wall being substantially inhibited by the thickness thereof to confine migration of such material during the operation of said cathode substantially through said cover sheet to the emitting surface formed thereby.

2. A cathode-according to claim 1, wherein said cover sheet is made of a material of the class of molybdenum.

3. A cathode according to claim 1, wherein said cover sheet is made of a material of the class of molybdenum, the thickness of said sheet being on the order of several tenths of one millimeter.

4. A cathode according to claim 3, comprising a tubular holder extending from said retaining wall, and a heater disposed within said holder for heating said receptacle to heat said emissive material so as to cause migration thereof through said cover sheet to the emitting surface formed thereby.

References Cited in the file of this patent UNITED STATES PATENTS 2,175,345 Gaidies Oct. 10, 1939 2,452,075 Smith Oct. 26, 1948 2,460,739 Francis Feb. 1, 1949 2,640,949 Cook June 2, 1953 2,640,950 Cook June 2, 1953 2,647,216 Brown July 28, 1953 2,673,277 Lemmens et a1. Mar. 23, 1954 2,687,489 Anderson et al Aug. 24, 1954 

